Curl-crested Manucode

Koala

Small, herbivorous koalas can create an awful lot of noise during the breeding season. These Australian marsupials are not bears. Nor are they friendly. Once hunted to near extinction, the population eventually rebounded. Now, they're threatened by habitat loss and urbanization, as well as a form of chlamydia that has caused symptoms such as blindness and infertility in as much as 50 percent of the population.

Walrus

The ruckus you hear is the sound of a walrus (Odobenus rosmarus) hammering his tusks on ice. This is also one of audio curator Greg Budney's favorite recordings. "The walrus is absolutely astonishing," Budney says. "It floored me the first time I heard it."

Tui

The tui (Prosthemadera novaeseelandiae) is a colorful, aggressive bird that lives in New Zealand and feeds on flower nectar, insects, and seeds. Like parrots, tuis can mimic human speech and repeat complicated phrases. Their normal calls, though, include a cacophony of wheezes, bells, clicks, and groans.

Tasmanian Devil

Kind of like a cross between a pig, bear, and dog, the Tasmanian Devil (Sarcophilus harrisii) is the source of these distressing vocalizations. It's not as mean as it sounds, though. The bad news: This carnivorous marsupial is endangered, and populations are extremely threatened by a transmissible cancer that causes facial tumors and kills within months.

Snowy Owl

Montezuma Oropendola

The coastal Caribbean rainforests are home to the Montezuma Oropendola (Psarocolius montezuma), a large, colorful bird whose song sounds a lot like a gurgling extraterrestrial. Much larger than the females, males attempt to woo mates with this unearthly song -- accompanied by a courtship display that sometimes includes singing while hanging upside down from tree branches.

Indri lemur

If it sounds like the forests of Madagascar are ringing with the polyphonic tones of a jazz quartet, look to the trees: It could be the songs of the endangered Indri lemur (Indri indri). These large tree-dwellers sing to one another to attract mates, defend territories, and solidify family groups.

Indris are monogamous, and sleep high in the trees through which they make their way during the day, leaping and climbing, in search of flowers, fruits, seeds, and bark.

Great Potoo

Larger than the common potoo, the great potoo (Nyctibius grandis) is the biggest of the potoo species. Its cryptic plumage helps it remain camouflaged during the day -- it blends in well with the trees in which it perches -- and it hunts for insects at night.

But unlike its common cousin, the great potoo does not sing a melodic song. Instead, these snorty grunts and growls belie the presence of this tropical bird.

Giant Otter

Carnivorous giant otters (Pteronuro brasiliensis) swim in South American rivers, with the largest population centered around the Amazon’s murky waters.

Among the noisiest of otters, the mammals’ vocalizations -- including grunts, snorts, barks, and whistles -- help them defend territories and communicate with family groups, which can include more than a dozen members.

Giant otters, growing up to 6 feet long, are sometimes referred to as “River Wolves.” They prefer to eat fish (including piranhas), but will also feast on crabs, small caimans, and snakes (including anacondas).

As bad-ass as they are, giant otters face a number of threats. In 1999, the IUCN listed giant otters as endangered; now there are just a few thousand individuals left. For years, the otters’ velvety pelts had made them a prize for poachers; now, habitat destruction and fragmentation also pose a threat, with roughly 80 percent of their South American range already gone.

Common Potoo

This nocturnal bird lives in Central and South America, producing songs that sound as though they're played by reed flutes. During the day, the common potoo (Nyctibius griseus) does its best impersonation of a tree stump, remaining very still and camouflaged on its perch.

In the evenings, the common potoo hunts for insects, its large yellow eyes peering through the darkness.

Common Loon

Sounding remarkably like a howling wolf, the common loon (Gavia immer) creates these haunting sounds as it flies. Known as a "diver" in Europe, the red-eyed bird can plunge to depths of 200 feet in search of fish. Clumsy and awkward on land, the common loon is graceful in the air and can reach speeds of 75 miles per hour while migrating.

Common Eider

Sounding pleasantly, perpetually surprised, the common eider (Somateria mollissima) produces a call that's commonly described as "ah-ooo." This seafaring duck breeds in the Arctic and frequents the coasts of Northern Europe, Siberia, and North America.

Large and social, the common eider forms colonies that can contain more than 15,000 individuals. It's best known for its down, plucked from the female. The duck dives for crustaceans and molluscs, and will eat mussels whole.

Brown Sicklebill

Instead of a machine gun, that's the song of a large bird of paradise called the Brown Sicklebill (Epimachus meyeri). These birds, which can reach 96 centimeters -- about three feet -- long, live in the mountain forests of New Guinea.

Alston's Brown Mouse

Sounding rather like a cricket, bird, or dolphin, Alston's brown mouse (Scotinomys teguina) serenades the highland forests of Central America. Also called the singing mouse, this tiny rodent feeds on beetles and other insects, and is active during the day.

Both males and females sing, sometimes entering into long duets. While singing, the mice sit on their hind legs and face the sky, producing a song that contains both audible and ultrasonic notes.

Black Howler Monkey

More like a metallic roar than a baying howl, these are the sounds of the black howler monkey (Alouatta caraya), a New World primate that lives in central South American forests. The calls, unleashed around dawn, are thought to help these social monkeys avoid conflict.

The 20-pound monkeys are omnivorous, preferring to dine on fruits and leaves in the treetops lining streams. Among the larger of South American primates, black howlers are also among the least active, sometimes spending more than two-thirds of the day lying around, digesting food.

Bearded Seal

These eerie, mournful-sounding whistles are the vocalizations of bearded seals (Erignathus barbatus) that live in the Arctic Ocean. Males' songs can be heard for miles; researchers are still not sure if the songs are used to attract mates or defend territories -- or both. As the males trill and moan, they dive in a loose spiral-shaped pattern, releasing bubbles and these distinctive, alien-sounding songs.

Named for their long whiskers, bearded seals can reach up to 8 feet in length. They feed mostly on crustaceans, squid, and fish -- and attempt to avoid becoming food for polar bears, walrus, and killer whales.

American Alligator

Native to the southeastern United States, American alligators (Alligator mississippiensis) are perched atop their food webs. Once endangered, these massive reptiles now number in the millions, lurking in lakes and streams and waiting for a meal to wander by. Though large and armored, alligators prefer to dine on fish and turtles, smaller mammals, and the occasional wild boar.

Alligators can reach lengths of up to 15 feet, weigh 1,000 pounds, and live for 50 years. Sex determination in offspring depends on the temperature at which the eggs are incubated: Warmer temperatures produce males, cooler temperatures, females.

Even though they don't have any vocal cords, male alligators bellow to attract females and warn off other males; they do this by inhaling air and releasing it in a deep-toned roar.

The murmurs, whispers, shrieks and growls of 9,000 species are now digitized in a huge library of animal sounds, including some songs that will never be sung again.

Housed at the Cornell Lab of Ornithology, the Macaulay Library’s audio archive contains roughly 150,000 high-resolution recordings, all available online. It’s the largest collection of wildlife sounds in the world, and routinely called upon by students, scholars, scientists, and filmmakers.

“Sound has a remarkable ability to transport someone,” said audio curator Greg Budney. “You play a sound, and it’s as though the person or the animal is alive, right there in the room with you.”

Digitizing the collection took 12 years. Now, the 10 terabytes of tracks have a total playback time of more than 7,500 hours. Supplementing that auditory cacophony are thousands of video clips, and a photo archive is on the way.

Also tucked into the collection are recordings of the now-extinct Kauai Oo and the (most-likely) extinct ivory-billed woodpecker. Preserving these natural sounds for future generations is certainly one of the collection’s functions, but Budney points to others.

“If you want people to have an appreciation for places they might never go, or animals they’ve never seen, sound really makes it alive for them,” he said. “But then, also in the collection, are fantastic discoveries waiting to be made.”

Already, the collection has revealed geographic differences in the tunes some birds sing, and helped scientists identify new bird species; biologists are using the recordings to better understand animal behavior; and the decades of data can tell scientists how vocalizations have changed over the years.

But it’s not just for experts: Anyone can contribute to the collection, and anyone can listen to it.

Two of Budney’s favorite sounds include the substrate-based vibrations of treehoppers – tiny, crazy-looking insects that send signals zinging through the stems and branches on which they perch – and the wing-beats of the ruffed grouse, which can be heard up to a quarter-mile away. “It sounds like someone starting up an old VW bus,” he said.

A bell-like walrus, otherworldly bird song, the hidden realm of insects, “There are sounds like this going on all around the world,” Budney said. “And we’re just beginning to learn about them, just beginning to tap into them.”

Now, archivists are working on adding more than 50,000 raw recordings to the already-expansive repository, a favored resource of filmmakers. Ken Burns consulted the Macaulay Library holdings while creating his National Parks series. Harry Potter’s audio team needed help finding something that sounded like a hippogriff. And Skywalker Sound sought some audio help while working on The Incredibles.

Hidden in the collection are all kinds of gems. Here, we’ve compiled a few of our favorites in audio quiz format -- all are in the grid above. Have a listen, then scroll down in each slide to reveal which animal made which sound (the "view all" option is not recommended for this gallery).

Is that an interstellar spaceship? Are those haunting howls coming from a mammal? A bird? What on Earth sounds like…that?

For those wading into the archive on their own, Budney has a few tips: Search by animal, or by geographic area. The first search results returned for a species are the best recordings. Learn songs or sounds a few at a time. And enjoy!

“One of the potent aspects of this archive that moves it out of the realm of just being a menagerie of wildlife sounds and into a real conservation and research resource is that technology is advancing our understanding of how animals use sounds,” Budney said.